Effects of Hydrostatic Pressure on Catalysis by Different Lactate Dehydrogenase Isozymes from Tissues of an Abyssal Fish

Abstract

SYNOPSIS. The predominant lactate dehydrogenases (LDH's) occurring in liver, heart, and muscle of a benthic Coryphaenoides species are electrophoretically distinguishable from each other. Maximum rates of pyruvate reduction catalyzed by heart and muscle LDH's show an optimum pH near neutrality, while liver LDH activity displays an unusual alkaline pH optimum. Pyruvate saturation curves are Michaelis-Menten in form for all three preparations. Maximum catalytic rates and the apparent K_m (pyruvate) are pressure independent for liver and heart LDH's. In the case of muscle LDH's, the maximum catalytic rate is also pressure insensitive, but the K_m is dramatically increased by pressure. These experiments dearly indicate that, at low substrate concentrations, the precise effects of pressure on enzyme-catalyzed reactions depend upon the nature and origin of the catalyst.